Yarn for vessle stent

ABSTRACT

A stent for a vessel implanted in the vessel of the living body including a main body portion of the stent formed into a tube by a yarn formed of a biodegradable polymer exhibiting a shape memory function. The main body portion of the stent is shape-memorized to a size that can be inplanted in the vessel. The main body portion of the stent is implanted in the vessel of the living body as it is contracted in diameter by an external force, and is enlarged in diameter by being heated with the temperature of the living body. The main body portion of the stent is formed by winding a yarn formed of a biodegradable polymer in a tube form as the yarn is bent in a zigzag design. The main body portion of the stent is enlarged or contracted in diameter with the bends of the yarn as the displacing portions.

TECHNICAL FIELD

[0001] This invention relates to a stent for the vessel mounted in thevessel, such as blood vessel, lymphatic vessel, bile duct or urinaryduct to maintain a constant state in the lumen of the vessel.

BACKGROUND ART

[0002] Heretofore, if a stenosis portion has occurred in the vessel of aliving body, in particular the blood vessel, such as artery, a balloonforming portion provided in the vicinity of the distal end of theballoon catheter is inserted into this stenosis portion. This balloonforming portion is expanded to form a balloon to expand the stenosisportion of the blood vessel to improve the blood flow, by way of thetranscutaneous blood vessel forming technique (PTA).

[0003] It has been clarified that, if the PTA is applied, stenosis tendsto be produced at a high probability in the once stenosis portion.

[0004] In order to prevent this restenosis, the current practice is toapply a tubular stent in the site processed with the PTA. This stent isinserted into the blood vessel in a diameter-contracted state andsubsequently implanted in the blood vessel as it is expanded in diameterto support the blood vessel from its inside to prevent restenosis frombeing produced in the blood vessel.

[0005] As this sort of the stent, there have so far been proposed aballoon expanding stent and a self-expanding stent.

[0006] The balloon expanding stent is applied over a balloon provided ina folded and diameter-contracted state in a catheter and, after beinginserted in the targeted site for implantation, such as a site oflesion, where the blood vessel is stenosis, the balloon is expanded andincreased in diameter to support the inner surface of the blood vessel.Once expanded in diameter, the balloon expanding stent is fixed in thisexpanded state and cannot be deformed in keeping with the pulsations ofthe blood vessel wall. On the other hand, if the balloon expanding stentis deformed after being expanded in diameter and implanted in thiscondition in the blood vessel, it cannot be restored to its originalexpanded state, such that there is the risk that the stent cannotsupport the inner surface of the blood vessel reliably.

[0007] The self-expanding stent is housed in the diameter-contractedstate in a holder, such as a tube, having an outer diameter smaller thanthe inner diameter of the targeted site for implantation in the bloodvessel, and is inserted in the targeted site for implantation in theblood vessel as it is housed in a holder. The stent, thus inserted inthe targeted site for implantation in the blood vessel, is extruded orextracted from the holder so as to be expanded in diameter to thepre-contracted state, by exploiting the force of restoration proper tothe stent, thus continuing to support the inner wall of the bloodvessel.

[0008] As this sort of the self-expanding stent, there is proposed sucha one obtained on warping a linear member of metal, such as stainlesssteel, into a sinusoidal or zigzag design, to form a tube.

[0009] With the self-expanding stent formed from a metal linear member,the outer diameter prevailing at the time of expansion is difficult tocontrol precisely, such that the stent is likely to be expandedexcessively in comparison with the inner diameter of the blood vessel inwhich it is implanted. Moreover, if the force of holding the stent inthe contracted state is removed, the stent is expanded abruptly. If thestent inserted into the blood vessel is expanded abruptly, the innerwall of the blood vessel is likely to be injured.

[0010] As the self-expanding stent, those formed of shape memory alloys,such as T—Ni, Ti—Ni—Cu or Ti—Ni—Fe based alloys, have been proposed.

[0011] The stent, formed of shape memory alloys, is kept to its sizewhen it is implanted in the targeted loading site in the blood vessel,by the shape memory action, and is subsequently contracted in diameter,so as to be inserted in this diameter-contracted state in the bloodvessel. After insertion into the targeted loading site in the bloodvessel, this stent is expanded to the size of the shape memory andsubsequently exhibits super-elasticity under the body temperature of theliving body to continue supporting the inner wall of the blood vessel.

[0012] Since the shape memory alloy has extremely high tenacity, suchthat it exerts an extremely large mechanical pressure to a portion ofthe inner wall of the blood vessel, thus possibly damaging the bloodvessel. Moreover, there are occasions wherein the stent formed of ashape memory alloy is not uniformly expanded in diameter against theinner wall of the blood vessel when implanted in the blood vessel. If aportion of the stent compresses against the inner wall of the bloodvessel prematurely to commence to be expanded in diameter, the bloodvessel cannot be expanded uniformly. In this case, the portion of theblood vessel, against which a portion of the stent has compressedprematurely, is enlarged excessively in diameter, and hence is likely tobe damaged.

[0013] The stent formed of metal such as shape memory alloy, onceimplanted in the vessel, such as blood vessel, is permanently left inthe living body unless it is taken out by surgical operations.

DISCLOSURE OF THE INVENTION

[0014] It is an object of the present invention to provide a stent for avessel, such as blood vessel, which is able to keep the vessel in theexpanded state reliably without injuring the vessel.

[0015] It is another object of the present invention to provide a stentfor a vessel which disappears after lapse of a pre-set period afterimplantation in the vessel to eliminate the necessity of executing asurgical operation of taking out the stent from the vessel afterrestoration of the site of lesion.

[0016] It is another object of the present invention to provide a stentfor a vessel which is able to support the vessel, such as blood vessel,with a uniform force.

[0017] It is yet another object of the present invention to provide astent for a vessel which can be inserted into a meandering vessel, suchas blood vessel, with good trackability, and which can be easily andreliably implanted in the targeted site in the vessel.

[0018] For accomplishing the above object, the present inventionprovides a stent for a vessel implanted in the vessel of the living bodyincluding a main body portion of the stent formed into a tube by a yarnformed of a biodegradable polymer exhibiting a shape memory function.The main body portion of the stent is shape-memorized to a size that canbe retained in the vessel. The main body portion of the stent isimplanted in the vessel of the living body as it is contracted indiameter by an external force, and is enlarged in diameter by beingheated with the body temperature of the living body.

[0019] The yarn used is a concatenated continuous monofilament yarn or amultifilament yarn made up of a plurality of monofilament yarns unifiedtogether.

[0020] The main body portion of the stent is formed by the yarn formedof a biodegradable polymer being wound to a tube as the yarn is bent ina zigzag design and is enlarged or contracted in diameter with the bendsof the yarn as displacing portions.

[0021] In the main body portion of the stent, at least part ofneighboring bends of the yarns wound to a tube as the yarns are bent ina zigzag design are connected to one another so that a pre-set tubularshape of the main body portion of the stent is positively maintained oncontracting or enlarging its diameter.

[0022] The tubular main body portion of the stent is formed by arrayingplural yarns each connected to form a ring as each yarn is bent in azigzag design, these yarns being juxtaposed along the axial direction ofthe main body portion of the stent to form a tube.

[0023] Each yarn making up the main body portion of the stent is formedof a biodegradable polymer having the glass transition temperature nothigher than approximately 70° C. Thus, the main body portion of thestent is enlarged in diameter to its shape-memorized state at atemperature close to the body temperature.

[0024] Each yarn making up the main body portion of the stent is formedof a biodegradable polymer compounded from one or more of polylacticacid (PLLA), polyglycolic acid (PGA), a copolymer of polyglycolic acidand polylactic acid, polydioxanone, a copolymer of trimethylenecarbonate and glycolid, and a copolymer of polyglycolic acid orpolylactic acid and ε-caprolactone.

[0025] If an radiopaque medium is mixed into or deposited on the yarn,the state of implantation of the stent in the vessel can be easilychecked from outside the living body using X-rays.

[0026] If antithrombotic drugs or drugs for suppressing neointimalformation are mixed into or deposited on the yarn formed by thebiodegradable polymer, these drugs can be administered in a sustainedfashion as the stent is dissolved.

[0027] Moreover, if a radiation source radiating β-rays or a radiationsource radiating γ-rays is mixed into or deposited on the yarn formed ofthe biodegradable polymer, these rays can be radiated to the lesion asthe stent is inserted into the living body, thus assuring sustainedirradiation of rdiation rays.

[0028] Other objects and advantages of the present invention will becomeapparent from the following description which is made with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a plan view showing a stent for the vessel according tothe present invention.

[0030]FIG. 2 is a perspective view showing a yarn constituting the stentaccording to the present invention.

[0031]FIG. 3 is a perspective view showing another yarn constituting thestent according to the present invention.

[0032]FIG. 4 is a plan view showing the bent state of the yarnconstituting a main body portion of the stent.

[0033]FIG. 5 is an enlarged plan view showing a portion of the main bodyportion of the stent.

[0034]FIG. 6 is a perspective view showing the state of how shape memoryis afforded to the stent for the vessel.

[0035]FIG. 7 is a perspective view showing the state of diametercontraction of a stent for vessel in shape memory to the diameterexpanded state.

[0036]FIG. 8 is a plan view showing the bent state of the yarn when thestent for vessel is contracted in diameter.

[0037]FIG. 9 is a plan view of the stent for vessel showing itsdiameter-contracted state.

[0038]FIG. 10 is a graph showing temperature characteristics of thestent for vessel according to the present invention.

[0039]FIG. 11 is a perspective view showing another embodiment of thestent for vessel according to the present invention.

[0040]FIG. 12 is a side view showing the state in which the stent forvessel according to the present invention is inserted into the bloodvessel.

BEST MODE FOR CARRYING OUT THE INVENTION

[0041] Referring to the drawings, a stent 1 for the vessel according tothe present invention is explained in detail.

[0042] The stent 1 for the vessel according to the present invention isused as it is inserted into the blood vessel such as coronary artery ofa living body and includes a tubular main body portion 3 of the stentcomprised of a yarn 2 of a biodegradable polymer having the shape memoryfunction, as shown in FIG. 1.

[0043] The yarn 2 is formed of a biodegradable polymer which does notaffect the living body when the yarn is implanted in a living body, suchas a human body. As this biodegradable polymer, polylactic acid (PLLA),polyglicolic acid (PGA), polyglactin (copolymer of polyglycolic acid andpolylactic acid), polydioxanone, polygliconate (copolymer oftrimethylene carbonate and glicolid), or a copolymer of polyglicolicacid or polylactic acid and ε-csaprolactone. It is also possible to usea biodegradable polymer obtained on compounding two or more of thesematerials.

[0044] The yarn 2 of the biodegradable polymer may be formed using ascrew extruder. For forming the yarn 2 using the screw extruder, pelletsformed of a biodegradable polymer as a starting material are heated at atemperature not higher than the melting point Tm and dried in vacua. Thepellets are charged into a hopper of the screw extruder and melted undercompression and heating to a temperature in the vicinity of the meltingpoint Tm or a temperature not lower than the melting point and nothigher than the thermal decomposition point. This melted biodegradablepolymer is extruded from a nozzle set at a temperature not higher thanthe melting point Tm and not lower than the glass transition temperatureTg. This extruded biodegradable polymer is rolled up to form a linearmember which then is further stretched to form the yarn 2 employed inthe present invention.

[0045] The yarn 2 thus formed is a monofilament yarn comprised of aconcatenation of the biodegradable polymer, as shown in FIG. 2.

[0046] The yarn 2 employed in the present invention may not only be themonofilament yarn but a multifilament yarn comprised of pluralmonofilament yarns 2 a, as shown in FIG. 3.

[0047] The yarn 2 formed by the aforementioned screw extruder using thebiodegradable polymer as explained above, is composed of cross-linkedpolymer molecules and exhibits shape memory properties.

[0048] The yarn 2 employed in the present invention may not only be of acircular cross-section but also of a flat cross-section.

[0049] The yarn 2, formed as explained above, is bent in a zig-zagdesign in concatenated vee shapes and wound spirally to constitute atubular main body portion of the stent 3 as shown in FIG. 4. A spirallywound shape of the yarn 2 is obtained with a side of a bend 4 of the veeshape as a short portion 4 a and with its opposite side as a longportion 4 b. By setting the lengths of the short portion 4 a and thelong portion 4 b between the bends 4 so as to be approximately equal toeach other, the apices of the neighboring bends 4 are contacted witheach other, as shown in FIG. 5. Part or all of the apices of thecontacted bends 4 are bonded to one another. The yarn 2 of the main bodyportion of the stent 3 is positively maintained in the state of keepingthe tubular shape by bonding the apices of the bends 4 contacting witheach other.

[0050] The bends 4 having the apices contacting with each other arebonded together by melting and fusing the contact portions together onheating the contact portions to a temperature not lower than the meltingpoint Tm.

[0051] The stent 1, constituted using the tubular main body portion ofthe stent 3, is shape-memorized to the size with which it is implantedin the blood vessel. For realizing this shape memory, the stent 1 isequipped on a shaft-like mold frame 101 sized to maintain the size ofthe stent 1 implanted in the vessel of the living body, and is heated toa temperature not lower than the glass transition temperature Tg and nothigher than the melting point of the biodegradable polymer constitutingthe yarn 2, so as to be deformed to a size consistent with the size ofthe mold frame 101. The stent 1 equipped on the mold frame 101 then iscooled, along with the mold frame 101, to a temperature not higher thanthe glass transition temperature Tg. This affords to the stent 1 theshape memory properties so that the stent is fixed in the deformedstate.

[0052] The heating for deforming the stent 1 to afford shape memorythereto is achieved by a heating oven.

[0053] The stent 1, obtained in this manner, is shape-memorized to thediameter R1 of approximately 3 to 5 mm and to the length L1 of 10 to 15mm, as shown in FIG. 1. This size corresponds to or is larger than thediameter with which the stent is implanted in the blood vessel of theliving body.

[0054] The stent 1 equipped and shape-memorized on the mold frame 101 iscontracted in diameter after it is dismounted from the mold frame 101.This contraction in diameter occurs as the main body portion of thestent 3 is deformed under a mechanical force applied from the outerperimeter of the main body portion of the stent 3 in the state in whichthe stent is cooled to a temperature not higher than the glasstransition temperature Tg. The diameter contraction of the stent 1 isrealized by thrusting the main body portion of the stent 3 into adiameter-contracting groove 202 provided in a diameter-contracting moldframe 201 as shown in FIG. 7. This diameter-contracting groove 202 isformed as a recessed groove in the major surface of thediameter-contracting mold frame 201 to permit facilitated insertion ofthe elongated stent 1.

[0055] The stent 1, thus pushed into the inside of thediameter-contracting groove 202, is contracted in diameter by displacingthe bends 4 so that the opening angle θ1 of the bend 4 will be a smalleropening angle θ2, as shown in FIG. 8. This diameter contraction,achieved by displacing the bends 4, is by deforming the bends 4 of theyarn 2 cooled to a temperature not higher than the glass transitiontemperature Tg. For example, in the stent 1, shape-memorized to thediameter R1 of approximately 3 to 5 mm, the diameter is reduced to adiameter R2 of approximately 1 to 2 mm, as shown in FIG. 9.

[0056] By this diameter contraction, the stent 1, shape-memorized to thediameter-expanded state, is slightly elongated in the longitudinaldirection from the shape-memorized state.

[0057] The stent 1, pushed into the diameter-contracting groove 202provided in the diameter-contracting mold frame 201, and therebycontracted in diameter, is pulled out from an opened end 203 of thediameter-contracting groove 202. The stent 1, produced from the yarn 2formed of the biodegradable polymer, is kept after dismounting from thediameter-contracting mold frame 201 at a temperature not higher than theglass transition temperature Tg to maintain the strain afforded to thebends 4 representing the displacement portions to keep thediameter-contracted state.

[0058] For contracting the diameter of the stent 1, shape-memorized tothe diameter-enlarged state, it is possible to use a variety ofdifferent methods other than the above-described method of employing thediameter-contracting mold frame 201. For example, the stent 1 may becontracted in diameter by applying a mechanical force from the outerperimeter of the shape-memorized stent 1 without using mold frames.

[0059] If the stent 1, contracted in diameter by application of anexternal force, is heated to a temperature not lower than the glasstransition temperature Tg, it is relieved of the strain afforded to thebends 4, so that the bend 4 folded to the small opening angle θ2 isopened to the opening angle θ1 to restore to its originalshape-memorized size. That is, the stent 1 on being re-heated to atemperature not lower than the glass transition temperature Tg isenlarged to its original shape-memorized size, as shown in FIG. 1.

[0060] Meanwhile, the stent 1 for the vessel, according to the presentinvention, is used as it is inserted into the blood vessel, such as thecoronary vessel of the living body, and is enlarged in diameter to theshape-memorized state, when inserted into the blood vessel, to supportits inner wall. It is noted that the yarn 2, making up the main bodyportion of the stent 3 of the stent 1 for the vessel, is formed of abiodegradable polymer, with the glass transition temperature Tg nothigher than 70° C., in order to restore to its original shape by thetemperature equal or close to body temperature of the living body.

[0061] The stent 1, formed by the yarn 2, which has the glass transitiontemperature Tg not higher than 70° C. and which is able to restore toits original shape by the body temperature of the living body, can beheated at a temperature not producing heat damages to the blood vesselof the living body, even if it is heated for enlarging its diameter toits shape-memorized state.

[0062] The stent 1, implanted on the blood vessel in thediameter-contracted state, is enlarged in diameter to realize the sizecapable of contacting with the inner wall of the blood vessel by aballoon provided on a catheter. On diameter expansion into contact withinner wall of the blood vessel by the balloon, the stent 1 can be evenlycontacted with the inner wall of the blood vessel and heated evenly bythe body temperature to restore to its original shape.

[0063] If the heated contrast medium is injected into the balloonthrough a catheter to restore the stent 1 to its original shape, theheating temperature of approximately 50° C. suffices, thus not producingheat damages to the blood vessel.

[0064] The temperature dependency in shape restoration of the stent 1formed by the yarn 2 of polylactic acid (PLLA) with the glass transitiontemperature Tg of approximately 57° C., and the stent 1 formed by theyarn 2 of polyglycolic acid (PGA) with the glass transition temperatureTg of approximately 37° C. was indicated.

[0065] The yarn 2 was produced as a stretched monofilament yarn, with adiameter of 50 to 300 μm. using the above-described screw extruder frompolylactic acid (PLLA) and polyglycolic acid (PGA). Using this yarn 2,each stent 1 is formed by bending in a zigzag design as explained aboveand is wound to a tube with a diameter R1 of 4 mm by shape memoryaction. The tube thus produced was then contracted to the diameter R2 of1.4 mm. Each stent 1 in the shape-memorized state is of a length L1 of12 mm.

[0066] The stent 1, formed by the yarn 2 of polylactic acid PLLA,restores to its original shape at 70° C. in only 0.2 sec, as shown at Ain FIG. 10, while recovering its shape at 50° C. in 13 sec andmoderately recovering itsshape at 37° C. close to the body temperatureover approximately 20 minutes. At 20° C. or less, close to the roomtemperature, the stent 1 is kept in the diameter-contracted statewithout recovering the shape.

[0067] Thus, with the stent 1, formed from the yarn 2 of polylactic acidPLLA, the time needed in shape restoration can be controlled bycontrolling the heating temperature. Therefore, the rate of shaperestoration can be controlled in keeping with the state of the bloodvessel in which is implanted the stent 1.

[0068] On the other hand, the stent 1, formed from the yarn 2 ofpolyglycolic acid (PGA), restores to its original shape at 45° C. inonly 0.5 second, as shown at B in FIG. 10, while restoring to itsoriginal shape in about a second at 37° C. close to the body temperatureand in 10 seconds at 30° C. lower than the body temperature. At 15° C.or less, close to room temperature, the diameter-contracted state ismaintained without shape recovery.

[0069] The stent 1 formed by the yarn 2 of polyglycolic acid (PGA),having a low glass transition temperature Tg, restores to its originalshape rapidly by body temperature on insertion into the blood vessel.Thus, the stent 1 can be applied with advantage to such application inwhich the stent needs to be enlarged in diameter as soon as it isinserted into the blood vessel. Moreover, since the stent can recover toits original shape promptly with the body temperature without heating,heat control for shape restoration of the stent 1 is facilitated.

[0070] In the stent for vessel 1, described above, the sole yarn 2, bentin a zigzag design for forming bends partway, is wound spirally to forma tubular main body portion of the stent 3. Alternatively, a sole yarn,bent in a zigzag design for forming bends partway, may be formed into aring, and a plurality of these yarns 21, wound into rings, may then bearrayed side-by-side along the axial direction to form a tubular mainbody portion of the stent 23, as shown in FIG. 11.

[0071] With this main body portion of the stent 23, the apex portions ofthe bends 24 of the respective juxtaposed yarns 21, contacting with eachother, are bonded together to maintain the tubular shape reliably.

[0072] The stent 1, comprised of the main body portion of the stent 23,is equipped on the shaft-like mold frame 101, as in the case of thestent 1 described above. The stent 1 of the present embodiment is againheated to a temperature not lower than the glass transition temperatureTg of the biodegradable polymer constituting the yarn 21 and not higherthan the melting point Tm, and is shape-memorized to a size with whichthe stent was implanted in the vessel of the living body. The stent thenis contracted to a diameter by e.g., a diameter-contracting mold frame201, which will allow the stent to be easily introduced into the vesselof the living body.

[0073] It suffices if the stent 1 of the present invention is formed asthe yarn 2 is bent in a zigzag design to a tube. A variety of methodsmay be used for winding the yarn in this manner.

[0074] Meanwhile, the shape memory restoring force of the shape memoryalloy used in a conventionally proposed stent is roughly tens ofkilograms (kg)/mm², whereas that of the biodegradable polymerconstituting the yarn of the stent according to the present invention isroughly several kg/mm². That is, the biodegradable polymer having theshape memory function has a shape memory restoring rest which isappreciably lower than that of the shape memory alloy. Moreover, therate of recovery to the shape-memorized state of the biodegradablepolymer having the shape memory function can be ten times that of theshape memory alloy. The stent formed using the yarn of the biodegradablepolymer having the shape memory function having these characteristicscan be restored to its original shape memorized state in a time intervalnot less than 10 times for the stent stent formed of the shape memoryalloy.

[0075] Thus, the stent formed of the yarn of the biodegradable polymerhaving such characteristics that the shape memory restoring force issmall and the time of restration to the shape memorized state is long,is enlarged in diameter evenly without abrupt increase in diameter, ifthe stent in the contracted-diameter state is inserted into the bloodvessel and subsequently enlatrged in diameter. Moreover there is no riskof excessive mechanical pressure being applied to the inner wall of theblood vessel, thus positively preventing the possibility of damaging theblood vessel.

[0076] On the other hand, the yarn formed of the biodegradable polymerhaving the shape memory function has a coefficient of friction smallerthan that of the linear member formed of metal, such as shape memoryalloy, so that, if the stent is abutted against a portion of the innerwall of the blood vessel during the time the stent is increased indiameter, it slips and expands uniformly on the inner wall surface ofthe blood vessel witout inflicting damages to the blood vessel.

[0077] It has been clinically demonstrated that, although a stent usedfor preventing restenosis of the blood vessel retains its shape forseveral weeks to several months after it is implanted in the bloodvessel, it desirably disappears in several months after implantation.

[0078] Since the stent according to the present invention is formed bythe yarn of a biodegradable polymer, it retains its shape for severalweeks to several months after it is implanted in the blood vessel of aliving body, however, it is absorbed into the living tissue to vanish inseveral months after it is implanted in the blood vessel.

[0079] A variety of drugs may be mixed into the yarn of the polymerfibers. If radiopaque agent is mixed at the time of spinning the yarn,the status of the stent for the vessel can be observed with X-rays, sothat thrombolytic drug or antithrombotic drug, such as heparin,urokinase or t-PA may be mixed into the yarn to prevent thromboticrestenosis of the blood vessel. Moreover, drugs can be continuouslyadministered. If a radiation source radiating β- or γ-rays is mixed intoor coated on the yarn, the lesion site in the living body can beilluminated by the radiations in a sustained and concentrated fashion.

[0080] Moreover, by admixing drugs aimed at suppressing the neointimalformation of the new inner film on the yarn, it is possible toadminister drugs aimed at suppressing the neointimal formation in asustained fashion.

[0081] It is noted that the radiopaque agent, thrombolytic drug orantithrombotic drug, pharmaceuticals aimed at suppressing the neointimalformation, or the radiation source, may also be coated on the surface ofthe spun yarn.

[0082] The stent 1 according to the present invention is constituted bywinding the biodegradable polymer yarns, having the shape memoryfunction, in a tube without overlapping, while it can be flexed anddeformed easily in the longitudinally, as shown in FIG. 12, and hencecan be inserted with good trackability into a bent blood vessel 301,because the stent 1 is formed by winding the yarns of the biodegradablepolymer having the shape memory function into a tube without the yarnsoverlapping with one another. In particular, the stent 1, formed using ayarn having bends partway, can be easily deformed in the longitudinaldirection and hence can be introduced into the bent blood vessel 301with high trackability.

[0083] On the other hand, the stent 1 of the present invention is formedwithout producing overlapping portions of the yarns 2, and can bedisplaced in the shape-memorized state with the bends 4 of the yarns 2as the displacing portions. Therefore, the stent 1 can restore its shapesmoothly without encountering the resistance by the overlapped yarns 2.

[0084] In addition, in the stent 1 of the present invention, in whichthe yarns 2 are wound without forming overlapping portions, there is nosuperposed yarns to reduce the damages otherwise inflicted to the wallof the blood vessel.

INDUSTRIAL APPLICABILITY

[0085] Since the stent for vessel according to the present invention isconstituted using a biodegradable polymer having the shape memoryfunction, the stent can memorize its shape to a size with which it isimplanted in the vessel, so that the vessel can be positively maintainedin the expanded state without being damaged.

[0086] Also, the stent can be easily enlarged in diameter after it isimplanted in the vessel, such as blood vessel, and also can support thevessel, such as blood vessel, with an even force, so that there may beprovided a stent for vessel that is able to hold the vessel in astabilized state in a reliably diameter-enlarged state.

[0087] In particular, since the stent for vessel according to thepresent invention is formed using a biodegradable polymer, it can retainits shape for several weeks to several months after it is implanted inthe blood vessel, however, the stent can vanish in several months afterit is implanted. Thus, the stent may be provided which is clinicallymost desirable.

1. A stent for a vessel used by being inserted into the vessel of theliving body, comprising: a main body portion of the stent formed into atube by a yarn formed of a biodegradable polymer exhibiting a shapememory function; said main body portion of the stent beingshape-memorized to a size that can be implanted in the vessel.
 2. Thestent for a vessel according to claim 1 wherein the yarn is aconcatenate continuous monofilament yarn.
 3. The stent for a vesselaccording to claim 1 wherein the yarn is a multi-filament yarn made upof a plurality of monofilament yarns unified together.
 4. The stent fora vessel according to claim 1 wherein said yarn is contracted indiameter by an external force and enlarged in diameter when implanted inthe vessel of the living body to its shape-memorized size.
 5. The stentfor a vessel according to claim 1 wherein said main body portion of thestent is formed by said yarn being wound to a tube as the yarn is bentin a zigzag design.
 6. The stent for a vessel according to claim 4wherein said main body portion of the stent is enlarged or contracted indiameter with said bends of the yarn as displacing portions.
 7. Thestent for a vessel according to claim 4 wherein, in said main bodyportion of the stent, at least part of the neighboring bends of the yarnare connected to each other.
 8. The stent for a vessel according toclaim 1 wherein said main body portion of the stent is formed byarraying plural yarns each connected to form a ring as each yarn is bentin a zigzag design, a plurality of said yarns being juxtaposed along theaxial direction of the main body portion of the stent to form a tube. 9.The stent for a vessel according to claim 8 wherein said main bodyportion of the stent is enlarged or contracted in diameter with saidbends of the yarn as displacing portions.
 10. The stent for a vesselaccording to claim 1 wherein said yarn is formed of a biodegradablepolymer having the glass transition temperature not higher thanapproximately 70° C.
 11. The stent for a vessel according to claim 1wherein said yarn is formed of one or more of biodegradable polymersfrom among polylactic acid (PLLA), polyglycolic acid (PGA), a copolymerof polyglycolic acid and polylactic acid, polydioxanone, a copolymer oftrimethylene carbonate and glycollide, and a copolymer of polyglycolicacid or polylactic acid and ε-caprolactone.
 12. The stent for a vesselaccording to claim 1 wherein said yarn is formed of a high polymercontaining one or more of a rediopaque agent, an antithrombotic drug,drugs for suppressing neointimal formation, a β-ray radiation source anda γ-ray radiation source.
 13. The stent for a vessel according to claim1 wherein one or more of a rediopaque, an antithrombotic drug, drugs forsuppressing neointimal formation, a β-ray radiation source and a γ-rayradiation source is deposited on the surface of said yarn.